Self-validating thermocouple

Abstract

Self-Validating Thermocouple (SVT) Systems capable of detecting sensor probe open circuits, short circuits, and unnoticeable faults such as a probe debonding and probe degradation are useful in the measurement of temperatures. SVT Systems provide such capabilities by incorporating a heating or excitation element into the measuring junction of the thermocouple. By heating the measuring junction and observing the decay time for the detected DC voltage signal, it is possible to indicate whether the thermocouple is bonded or debonded. A change in the thermal transfer function of the thermocouple system causes a change in the rise and decay times of the thermocouple output. Incorporation of the excitation element does not interfere with normal thermocouple operation, thus further allowing traditional validation procedures as well.

1. A thermocouple circuit, comprising:
 a reference junction; and 
 a measuring junction; 
 wherein the measuring junction is in thermal contact with an excitation element; 
 wherein the measuring junction is located within a first circuit path inhibiting an alternating current signal; 
 wherein the excitation element is located within a second circuit path providing an open circuit to a direct current signal; and 
 wherein the second circuit path is coupled in parallel with at least a portion of the first circuit path. 
 
     
     
       2. A thermocouple circuit, comprising:
 a reference junction; and 
 a measuring junction; 
 wherein the measuring junction is in thermal contact with an excitation element; 
 wherein the measuring junction is located within a first circuit path inhibiting an alternating current signal; 
 wherein the excitation element is located within a second circuit path providing an open circuit to a direct current signal; and 
 wherein the first circuit path comprises at least one inductor in series with the measuring junction. 
 
     
     
       3. The thermocouple circuit of  claim 2 , wherein the excitation element comprises a resistor. 
     
     
       4. The thermocouple circuit of  claim 2 , wherein the excitation element is in physical contact with the measuring junction. 
     
     
       5. The thermocouple circuit of  claim 2 , further comprising:
 wherein the second circuit path comprises at least one capacitor coupled in series with the excitation element. 
 
     
     
       6. The thermocouple circuit of  claim 2 , wherein the thermocouple circuit is of a J, K, E, or T type. 
     
     
       7. A thermocouple circuit, comprising:
 a reference junction; and 
 a measuring junction; 
 wherein the measuring junction is in thermal contact with an excitation element; 
 wherein the measuring junction is located within a first circuit path inhibiting an alternating current signal; 
 wherein the excitation element is located within a second circuit path providing an open circuit to a direct current signal; and 
 wherein the first circuit path and the second circuit path share a first lead for reading the measuring junction and applying the alternating current signal to the excitation element. 
 
     
     
       8. The thermocouple circuit of  claim 7 , further comprising:
 a first inductor coupled in series with the measuring junction; and 
 a first capacitor coupled in series with the excitation element. 
 
     
     
       9. The thermocouple circuit of  claim 8 , wherein the first inductor and the first capacitor are each coupled to the first lead. 
     
     
       10. The thermocouple circuit of  claim 8 , wherein the first inductor and the first capacitor are coupled in parallel. 
     
     
       11. The thermocouple circuit of  claim 8 , further comprising:
 a second inductor coupled in series with the measuring junction and the first inductor; and 
 a second capacitor coupled in series with the excitation element and the first capacitor. 
 
     
     
       12. The thermocouple circuit of  claim 11 , wherein the second inductor and the second capacitor are each coupled to a second lead. 
     
     
       13. A thermocouple system, comprising:
 a thermocouple circuit, wherein the thermocouple circuit comprises:
 a reference junction; and 
 a measuring junction; 
 wherein the measuring junction is in thermal contact with an excitation element; 
 wherein the measuring junction is located within a first circuit path inhibiting an alternating current signal; 
 wherein the excitation element is located within a second circuit path providing an open circuit to a direct current signal; and 
 wherein the first circuit path comprises at least one inductor in series with the measuring junction; 
 
 a pulse wave modulator coupled to provide an alternating current signal to the excitation element; 
 a cold junction compensator and signal conditioner circuit coupled to receive a detected voltage signal from the thermocouple circuit and to provide a compensated and conditioned voltage signal; 
 an analog to digital converter coupled to receive the compensated and conditioned signal and provide a digital signal representative of an expected temperature of the measuring junction; 
 a processor coupled to receive the digital signal; and 
 an interface coupled to be processor to provide input/output. 
 
     
     
       14. A thermocouple system, comprising:
 a thermocouple circuit, wherein the thermocouple circuit comprises:
 a reference junction; and 
 a measuring junction; 
 wherein the measuring junction is in thermal contact with an excitation element; 
 wherein the measuring junction is located within a first circuit path inhibiting an alternating current signal; 
 wherein the excitation element is located within a second circuit path providing an open circuit to a direct current signal; and 
 wherein the first circuit path comprises at least one inductor in series with the measuring junction; 
 
 a pulse wave modulator coupled to provide an alternating current signal to the excitation element; 
 a cold junction compensator and signal conditioner circuit coupled to receive a detected voltage signal from the thermocouple circuit and to provide a compensated and conditioned voltage signal; 
 an analog to digital converter coupled to receive the compensated and conditioned signal and provide a digital signal representative of an expected temperature of the measuring junction; 
 a processor coupled to receive the digital signal; and 
 an interface coupled to be processor to provide input/output. 
 
     
     
       15. The thermocouple system of  claim 14 , further comprising a power section to provide power to the various elements of the thermocouple system. 
     
     
       16. The thermocouple system of  claim 14 , wherein the second circuit path comprises at least one capacitor in series with the excitation element. 
     
     
       17. The thermocouple system of  claim 14 , wherein the thermocouple circuit is of a J, K, E, or T type. 
     
     
       18. The thermocouple system of  claim 14 , further comprising a memory coupled to the processor. 
     
     
       19. The thermocouple system of  claim 18 , wherein the memory is a non-volatile memory.